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    // 原型和原型链
    // 实例化对象 -> 构造函数.prototype -> Object.prototype -> null

    // var arr = [1, 2, 3];
    var s = new Set();
    // console.log(s);

    // toString()
    // valueOf()
    // isPrototypeOf()    instanceof
    // hasOwnProperty()   in
    // propertyIsEnumerable

    // console.log(Object.prototype.toString.call(s));

    // 面向对象继承













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